This invention relates to thermosettable allyl styryl pyridine and pyrazine compositions having improved processability and excellent thermal stability.
Hydroxystyryl pyridines are known from Yan et al, Org. Coatings and Applied Science Proceedings, 46:482-488 (ACS Preprint 183 National Meeting, Las Vegas, Nevada 1982); Chiang et al, J. Org. Chem., 10:21-25 (1945); Bramsch, Chem. Berichte, 42:1193-1197 (1909); Franke, Chem. Berichte, 38:3724-3728 (1905) and Ser. No. 588,597 filed Mar. 12, 1984 now U.S. Pat. No. 4,515,938 granted, May 7, 1985. The hydroxystyryl pyridines typically possess high melting points and low solvent solubility, hence conventional processing, such as impregnation of a fiberglass mat by hot melt or solvent impregnation techniques is extremely difficult. Hydroxyl groups present in the cured (thermoset) hydroxystyryl pyridines can induce moisture sensitivity and susceptibility to chemical attack by solvents as well as aqueous media such as dilute sodium hydroxide solution. Reactivity of the hydroxystyryl pyridines is poor, with prolonged cure temperatures of 250.degree. C. to 300.degree. C. or higher being required. The condensation curing reaction to provide a hydroxypolystyryl pyridine evolves water, hence voids and bubbles are typically present in the cured products. These defects are deleterious to the mechanical properties of the cured product.
More recently, vinyl styryl pyridines and vinyl polystyryl pyridines have been developed, for example as taught by Ratto, et al in U.S. Pat. No. 4,362,860. Said vinyl styryl pyridine compositions provide some improvement in reactivity, being initially cured at temperatures of 150.degree. C. to 200.degree. C., however, many of the aforementioned problems remain. The reaction times and reaction temperatures required for synthesis of vinyl styryl pyridines frequently dimish the polymerizable vinyl group content of the finished product thus leading to only an incremental improvement in reactivity.
Various other styryl pyridine compositions are known, however, these compositions typically possess the aforementioned problems.
The present invention provides novel thermosettable allyl styryl pyridine and/or pyrazine compositions having excellent processability being typically low melting, highly solvent soluble and highly reactive. Curing does not evolve gaseous products, such as water vapor, thus void-free cured products are readily obtained. All of these property improvements are obtained without a significant loss in thermal stability. The process of the present invention uses a transcarbonation reaction wherein allyl methyl carbonate stoichiometrically reacted with the hydroxystyryl pyridine and/or pyrazine provides essentially total allylation of the hydroxyl groups of the hydroxystyryl pyridine (pyrazine). Alternately, a direct allylation reaction is employed wherein an allyl halide is stoichiometrically reacted with the hydroxyl groups of the hydroxy styryl pyridine (pyrazine). These compositions are useful in the preparation of homopolymers or copolymers which can take form of unfilled or filled castings, fiberglass laminates, graphite or carbon fiber reinforced composites, coatings and the like.